Motor control.



W. C. STRANG.

MOTOR CONTROL.

APPLICATION FILED AUG-22. I913- 1 ,264,992. Patented May 7, I918.

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WALTER C. STRANG, 0F YONKERS, NEW YORK, ASSIGNOR TO OTIS ELEVATORCOMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

MOTOR CONTROL.

Application filed August 22, 1913.

To all whom it may concern:

Be it known that I, WALTER C. STRANG, a citizen of the United States,residing in Yonkers, in the county of VVestchester and State of NewYork, have invented a new and useful Improvement in Motor Controls, ofwhich the following is a specification.

My invention relates to the control of an electric motor, and has for anobject the provision of automatically operated means for preventing thetoo sudden reversal of the motor.

A further object of the invention is to prevent the closing of the motorcircuit, unless and until the starting resistance is inserted in thearmature circuit.

Other objects of the invention will appear hereinafter, the novelcombinations of elements being pointed out in the annexed claims.

Figures 1 and 2 of the drawing represent motor controlling systemscontaining an em bodiment of my invention.

In the control of an electric motor where it is required that the motorbe reversed, such for example as in an electric hoist or elevator, it isessential that the motor be safeguarded against a too sudden reversal bya careless operator. Various schemes have been proposed from time totime to overcome this danger, and, while such schemes will operate moreor less satisfactorily they are as a rule complicated and liable to getout of order, and are expensive to install. I propose to attain thedesired object. in a very simple and practical manner and withoutresorting to complicated or expensive apparatus.

Referring to Fig. 1, I show a hand controller C, operative to efi'ectthe closure of either of the reversing switches R or R, to close acircuit to the motor M. A starting resistance S is gradually shortcircuited by an accelerating magnet A and the motor is automatically runup to full speed in either direction of rotation. The acceleratingmagnet A is substantially like that shown in Patent No. 677,359, issuedto John D. Ihlder, July 2, 1901, and comprises the contacts 1, 2, 3 and4, which are arranged to operate successively in the order named toshort circuit the starting resistance according to the varying potentialof the motor armature.

The contact 1, or rather the arm which carries the contact, ispreterably made of less Specification of Letters Patent.

Patented May 7, 1918.

Serial No. 786,072.

weight than the other contacts 2, 3, and 4, so that it will be the lastone to fall out when the magnet is de'e'nergized. Movable with thecontact 1 is an insulated contact 5 which normally engages a stationarycontact 6 when the magnet A is completely dee'nergized. and is movedupwardly into electrical engagement with a stationary contact 7 when thecontact 1 operates to short circuit the first portion of the startingresist ance.

The operation of the device shown in Fig. 1 may best be shown byassuming the operator has moved the lever of the master switch C untilthe contact 8 is in electrical engagement therewith. A circuit may nowbe traced from the main through the contacts 5' and 6 to the switchlever, switch contact 8, magnet winding of reversing switch R. and bythe conductor 9 to the main.- The reversing switch operating circuitbeing complete. the switch operates to raise its core and connectedcontact disks, thereb) closing a circuit to the motor. The motor circuitmay be traced from the main. through the reversing switch contacts 10and 11. armature brush 12, through the motor armature to brush 13,reversing switch contacts 1% and 15, conductors 16, starting resistance3, to the main. The circuit to themotor field F is always closed throughthe high resistance 17 so that the motor field may be partiallymagnetized when the motor armature is disconnected from the line. Assoon as the reversing switch R closes, this resistance 17 is shortcircuited and the motor field at once attains full strength with itsterminals connected across the mains.

The circuit being now closed, the motor starts, and as itscounter-electro-motive force rises, the accelerating magnet A beingconnected across the armature brushes, gathers strength and successivelyoperates the contacts 1, 2, 3 and 4, in the order named, gradually toshort circuit the starting resistance S and allow the motor to reachfull speed. As soon as the contact 1 operates to short circuit the firststep of the starting resistance the contact 5 is moved out of engagcment with the contact 6 and is carried into engagement with the contactIn separating the contacts 5 and 6, it w1ll be observed that theconductor 18 leading to the master switch lever is open-circuited, whilethe closing of the contacts 5 and 7 establishes a circuit from the righthand terminal of the field winding F to the main which circuit is inparallel to the circuit closed from this same field terminal to the mainvia the conductor 19 and reversing switch contact 10. While it mightappear that the open circuiting of the contact 6 and conductor 18 wouldopen circuit the magnet of the reversing switch, such is not the case,since when the reversing switch operated, an additional circuit wasclosed from the main to the lever of the master switch through thereversing switch contacts 10 and 20, and the conductor 21 and hence thereversing switch remains in closed position.

If the operator attempts suddenly to reverse the motor by reversing themaster switch C, the motor will first come gradually to rest with itsfield fully excited from the mains via the contacts 5 and 7, and then,and not until then, cana circuit be closed to the motor in the reversedirection to effect a reversal. The reason for this is as follows: Assoon as the master switch lever leaves the contact 8, the circuit to themagnet of the reversing switch R is interrupted and this switchimmediately drops, thereby opening the motor armature circuit at thecontact 10, and rendering the contact 20 and conductor 21, which feedsthemaster switch, dead. Since the motor is still in motion a currentcontinues to pass from the motor, acti ng in the capacity of aseparately excitedgenerator, to the accelerating magnet A and thecontact 5 of said magnet remains out of engagement with the contact 6.Such being the case, both the conductors 21 and 18 which alternatelyserve as feed wires for the master switch are dead and it will beimpossible to close a circuit to either of the reversing switch magnetsas long as the motor possesses any appreciable speed. As soon as themotor substantially comes to rest, its generated electro-motive forcefalls to such an amount that the accelerating magnet nolonger hassufficient strength to maintain the contacts 5 and 7 invclosed positionand the contact 5 falls away from the contact7, and engages the contact6, whereupon a circuit may again be closed through the conductor 18 tothe magnet of reversin switch R or reversin switch R as desire As t ccontacts 5 and 7 become separated, the right hand terminal of the fieldF is no longer connected directly to the main, but is connected to themain through the conductor 19 and the high resistance 17. Hence thefield strength becomes weakened and a substantial saving in currentconsumption is the result.

The chief function of the contact 7 in the motor field circuit, is toinsure that the motor field will always be strongly excited when thearmature circuit to the mains is inserted in the armature circuit.

open and the motor is running. As long as the field is excited the motorcan always be depended upon to generate sufficient potential to maintainthe accelerating magnet contacts 5 and 6 in open relation even at verylow motor speeds, From this it follows that a reversing switch cannot bemoved to effect a reversal of the motor until the latter hassubstantially come to rest. Furthermore the motor cannot be reversed norcan it again be started in the same direction unless and until theentire starting resistance first be re- The reason for this lies in thefact that the accelerating contact 1 being of lighter construction thanthe contacts 2, 3 and 4, is the last one to drop out as the motor-comesto rest, hence the contacts 5 and 6 cannot close to permit the operatorto establish the motor circuit in either direction until after all ofthe contacts 4, 3', 2 and 1 first have effected the open oircuitin ofthe starting resistance.

While have shown the contact 7 arranged to maintain the field circuit ofthe motor at one strength while the motor is rotating, this contact mayin certain cases be dispensed with and the field may be permanentlyconnected to receive current at the full line potential. Or if desired,the field circuit may be broken at the reversing switches and one maydepend upon the uncertain and variable residual magnetism of the motorfield to excite the motor in slowing down and stop ping. Whether thecontact 7 is used or not depends upon the varying conditions found inpractice, but in general I prefer to use tain constant field strengthwhile the motor is actingas a enerator and hence the motor may be depened upon to generate an appreciable potential and current at very lowspeeds, so that a reversal of the motor cannot possible be effectedunless and until the mo.- tor first be substantially at rest, or at thevery least, rotating at such a slow speed that a reverse circuit maysafely be closed to the motor from the mains without any danger to themotor or parts drivenvtherefrom.

In Fig. 2 the arrangement is somewhat different than that just describedand is particularly adapted to the control of the motor of an electricelevator wherein an electric brake is employed to assist the motor instopping and holding the elevator car against movement when the motorcircuit is cut off. Referring to this view, it will be seen that themagnets of both reversing switches are connected to the main and to themaster switch. while the feed wire 23 of the master switch may beconnected through the accelerating magnet contacts 5 and 6 to the mainor by the normally open contacts 24: and controlled by the brake. Instarting the motor, the magnet of reversing switch R receives currentvia the contacts 5 and 6 one of which, the contact 6. is connected tothe main. As soon as the reversing switch It operates the motor circuitis completed, as before described in connection with Fig. 1, and thehigh resistance 17 in the field circuit is short circuited to permit offull field strength and the brake circuit is closed at the contact 10and contact disk 26. As soon as the brake lifts the brake contact 24 and25 are brought together. thereby establishing a short circuit around thecontacts 5 and G of the accelerating magnet and maintaining a circuitfor the magnet of the reversing switch after these latter contacts areseparated by the automatic operation of the accelerating magnet A. Ifthe operator attempts to reverse the motor, the circuit of the reversingswitch R is immediately opened and this switch operates to cut off thesupply to the motor and brake and the latter at once opens its contact24 and 25, thereby rendering the feed wire 23 of the master switch dead;the contacts 5 and 6 being previously separated by the motor actingthrough the accelerating magnet during the period of starting. The feedwire 23 of the master switch being dead it is obviously impossible againto operate either of the reversing switches. As the motor, assisted bythe brake, slows down to practically zero speed, the accelerating magnetallows the contacts 5 and 6 to engage each other and then, and not untilthen, can a circuit to either of the reversing switches be closed fromthe master switch.

In Fig. :2 it will be observed that the field is only partially excitedduring the slowing down or stopping period, since the field circuitincludes the high resistance 17 when the reversing switches are in opencircuit position, and this resistance not only effects an economy ofcurrent consumption while the motor is disconnected from the supplymain, but it also insures a field of predetermined strength during theslowing down and stopping period so that the motor must firstsubstantially be brought .to rest before the control of the motor can berestored to the master switch.

What I claim as new and desire to have protected by Letters Patent ofthe United States is l. The combination with an electric m0- tor ofreversing switches therefor, a resistance in the circuit of the motorarmature, a device controlled by the motor for cutting out saidresistance in starting, and means controlled by said device forpreventing the operation of either of said reversing switches until themotor substantially comes to rest.

2. The combination with an electric motor, of electro-responsivereversing switches for the motor, an operating circuit for saidswitches, a motor starting resistance, a device controlled by the speedof the motor for short circuiting said starting resistance, and meanscontrolled by said device for opening the operating circuit of'thereversing switcheswhile the motor is rotating.

3. The combination with an electric motor, of electro-responsive motorreversing switches, an operating circuit for said switches, and meansactuated by the motor while starting for maintaining said operatingcircuit open until the motor substantially comes to rest.

4. The combination with an electric motor, of reversing switchestherefor, a circuit for effecting the operation of said switches, andmeans actuated by the counter-electromotive force of the motor instarting for opening said operating circuit.and maintaining said circuitopen until the motor substantially comes to rest.

5. The combination with an electric motor, of reversing switchestherefor biased toward open position, a circuit for effecting theinitial operation of said switches, an additional circuit formaintaining said switches in closed position, and automatic means c011-trolled by the motor for opening said first named circuit to prevent theclosing of either of said reversing switches after said additionalcircuit is opened and the motor is rotating.

(i. In a system of motor control. the combination with an electricmotor, of electro responsive apparatus for effecting the reversal of themotor, and means dependent upon the motor in starting for controllingthe operating circuit of said electro-responsive apparatus to preventreversal of the motor before substantial reduction in speed thereof.

7. In a system of motor control, the combination with an electric motor,of electroresponsive apparatus for effectin the reversal of themotor,and means ependent upon the speed of the motor in starting forcontrolling the operating circuit of said electro-responsive apparatusto prevent a reversal of the motor before substantial reduction in thespeed thereof.

8. In a system of motor control, the combination with an electric motor,of reversing switches therefor, an electromagnet for operating eachswitch, and means operated by the motor in starting for controlling thecircuit of said electromagnets to prevent energization of the latterimmediately after one of said switches opens.

9. In a system of motor control, the combination with an electric motor,of reversing mechanism therefor, electric means for actuating thereversing mechanism, and a device controlled by the speed of the motorin starting for interrupting the circuit of said electric means toprevent a sudden change in the direction of rotation of the motorarmature.

10. In a system of motor control, the combination of an electric motor,reversing switches therefor, a circuit for effecting the closing ofoneof said switches, a circuit for maintaining said switch closed, andmeans for maintaining said first named circuit open during the periodthat the motor armature is rotating.

11. In a system of motor control, the combination of an electric motor,reversing switches therefor, a circuit for efiecting the closing of oneof said switches, a circuit for maintaining said switch closed, andmeans controlled by the motor for maintaining said first named circuitopen while the motor is in motion.

12. In a system of mot-or control, the combination of an electric motor,electroresponsive reversing switches, a starting resistance for themotor, a magnet arranged automati-- cally to control said resistance, acircuit to the magnets of the reversing switches, a self holding circuitto the magnets of the reversing switches controlled by said switches,and means for opening said first named circuit and for maintaining thesame open while the motor armature is in motion, and the said selfholding circuit is open to prevent a too sudden reversal of the motor.

13. The combination with an electric motor, of a resistance in the motorcircuit, a device for controlling said resistance, and means operated bysaid device for controlling a circuit to'the field of the motor and forpreventing a too sudden reversal of the motor.

14. The combination wlth an electric mocircuit of said switches and acircuit to the field winding of the motor for preventing a too suddenreversal of the motor.

15. The combination with an electric motor, of electro-responsivereversing switches therefor, an operating circuit for said switches, andmeans controlled by the motor in starting for maintaining said operatingcircuit open and the motor field ata predetermined strength while themotor is coming to rest.

16. The combination with an electric motor, of electro responsivereversing switches therefor, an operating circuit for said switches, andmeans operated by the motor in starting for maintaining said operatingcircuit open and the motor field at a predetermined strength while themotor is coming to rest.

17 The combination with an electric motor, of electro-responsivereversing switches therefor, an operating circuit for said switches, aresistance in the motor circuit, an automatic device for controllingsaid resistance, and means operated by said device for preventing theoperation of said reversing switches and for maintaining the motor fieldof predetermined strength while the motor is coming to rest.

In testimony whereof, I have signed my name to this specification in thepresence of two subscribing witnesses.

WALTER O. STRANG.

Witnesses:

ERNEST L. GALE, J12, ARTHUR Tnnzrsn, Jr.

